Birdcages are typically used in connection with the rear axles of high performance vehicles, such as race cars or sprint cars. Typically, the birdcages are located on either side of the vehicle and support a respective bearing structure. Each of the bearing structures communicates with an opposing end of the vehicle rear axle. This engagement between the bearings and the rear axle allows the rear axle to drive the rear wheels.
As the bearings within the birdcage support and communicate with a rotating structure to provide power to the rear wheels, timing of the birdcage is critical to proper vehicle performance and bearing longevity. It is well known that timing a birdcage means locating it vertically with respect to the ground (or as close to vertical as possible) to align the upper and lower birdcage bolts. Proper timing of the birdcage prevents uneven side-to-side loading on the radius rods during acceleration of the vehicle and the rear axle. As is known, timing is accomplished by adjusting the length of the connection of the torsion arm rod (at the bottom) and the length of the radius arm (at the top) to obtain verticality of the birdcage.
One common method for timing the birdcages includes raising the vehicle by positioning blocks under the rear lower frame rails and the rear axle to simulate the desired ride heights. This method also takes into account any stagger that may exist. Locating the chassis at the correct ride height prevents the unwanted variance of the angles of the two attaching arms. Once the vehicle has been properly elevated, the torsion bars on each side of the vehicle are disconnected. Thereafter, the radius rod length at the left rear is adjusted to properly orient the left rear birdcage in a vertical position. As will be appreciated by one of ordinary skill in the art, a carpenter's square and level is appropriate to assist in obtaining the desired vertical alignment of the birdcage. Alternatively, a birdcage level tool, such is made and sold by MPD Racing Products, may be utilized. Once the left rear birdcage is vertically aligned, the right rear birdcage must also be vertically aligned. Typically, at this point, the left and right sides are rechecked to ensure that they have not been moved out of alignment. Similarly, at this point, the axle squareness to the motor plate is also typically rechecked.
Once these components are all properly aligned, the left rear torsion arm is hooked up to the vehicle suspension while the left rear birdcage is maintained in a vertical position. Both sides are then again rechecked. If both birdcages are still vertical and the axle is still square to the motor plate, the right rear torsion arm is hooked up to the vehicle suspension while the right rear birdcage is maintained in a vertical position. Both sides are then again rechecked. As will be understood, while this process can result in the desired properly aligned chassis, it requires considerable time and effort.
Once the birdcages are timed, the squareness of the rear end to the motor plate is again rechecked as timing the birdcages can cause the axle orientation to change. If this occurs, the axle must be squared and the birdcages must be retimed. This is why typical processes recommend ensuring that the rear axles are square at each step as the arms are hooked up to the birdcages.
Once the birdcages are installed, the associated bearings located within each birdcage are subjected during use to significant side loads, particularly on the rear driver's side tire because of the angle or banking of the track as the vehicle is being driven. This side load or axial load exerts force, which is created by the movement of the axle with respect to the stationary birdcage and bearing. This movement of the axle in the bearing can cause the bearing to wear quickly and prematurely, as the bearing is being driven forwardly by the rotation of the axle. This is true regardless of the alignment of the birdcage. Moreover, because the bearing race is being subjected to both a forward and a side force, its operation can be inefficient, which can affect vehicle performance and driveability. Additionally, the bearing on the rear suspension can bind altogether in response to those side loads.
It would therefore be desirable to provide a birdcage assembly including a bearing that minimizes these problems, including bearing inefficiency and bind.